Why would you throw away your eggshells when they’re so useful?



Crushing egg shells with mortar and pestle


There are a myriad of ways to recycle them. My favourite is for soil improvement.

Years ago, I came across a gardening tip for reusing eggshells. Until recently, I hadn’t  given it a try.

The accepted wisdom seems to be that crushing discarded eggshells and digging them into the garden or adding them to your compost is an effective way to add minerals, especially calcium, to the soil. The shell of a chicken egg is comprised of about 96% calcium carbonate (CaCO3) crystals which are bound together by proteins. Calcium is essential for building strong plant-cell walls, enabling vigorous and rapid plant growth. Without it, plants like tomatoes, capsicums and squash for example, are likely to develop blossom-end rot, resulting in a failed crop.

Some advice is that crushed eggshells can deter pests like caterpillars, slugs and snails, which suffer a thousand tiny cuts when they crawl across the grit causing dehydration and eventual death – sounds gruesome! I can’t attest to this because I use my crushed eggshells in a more indirect way.

My compost worms love them!

I’ve written in the past about my worm farm and how vital the ‘worm tea’ and castings it produces are for soil health. Besides which, it’s a great recycling tool for eating up my kitchen waste, as well as old paper and cardboard.


Eggshell grit in the compost

I discovered that calcium provided by the eggshells, reduces high acid conditions in the worm farm which is detrimental to the worms and can make the farm smelly as well. Crushed eggshells also provide grit to aid the worms’ digestion. ‘And, it is believed that eggshells help worms in the reproductive process’ (ref). I have yet to verify this but since they are such prolific little critters, I’m not about to argue.

If you intend trying this on your worms, take care to crush the shells to a very fine grit. I use a mortar and pestle to grind them down. Since composting worms don’t have teeth, the grit must be small enough for them to swallow; apparently they need a bit of grit to help digest the food scraps.


It’s also important not to overdo adding eggshells to your farm. About a half cup of grit at a time is sufficient for most household worm farms to manage. Don’t add more until the previous batch is no longer visible. Any surplus I have is added to my citrus which seem to appreciate the extra dose of calcium.

I was a little concerned about using eggshells because of the possibility of introducing salmonella into the worm castings. Many sites advocate the washing or heating of eggshells before introducing them to the worm farm of compost. I do neither. But I am careful to wash my hands after gardening. The Michigan State University report is reassuring: ‘Egg shells are often such a small percentage of the whole, that rarely are they able to overwhelm a batch of compost. Overall, after the composting process is finished and cured, most pathogens will be brought to a similar level as the surrounding soil thus reducing the amount of salmonella bacteria in your compost.’

One of the most encouraging things I found while researching the benefits of egg shell to the soil, was how it’s been demonstrated (in a calcined form) to ‘mitigate the accumulation of antibiotics, heavy metals, antibiotic-resistant bacteria (ARB)/antibiotic resistance genes (ARGs) in vegetables [which] has become a new threat to human health’ (ref). In the study referenced, adding the modified egg shells to the soil of a growing bell pepper, impeded the uptake of pollutants like those mentioned above.

I can’t help thinking the answers to many of our pollution questions lie in nature herself. The microbes found to disseminate oil spills also comes to mind (ref).

“The human race is challenged more than ever before to demonstrate our mastery, not over nature but of ourselves.”
Rachel Carson



Further reading:





17 responses to “Eggactly!

  1. Good article.I to add mine to both my worm farm and compost as you pointed out it is best to grind before adding so I will now grind mine before adding.Thanks!

    Liked by 1 person

    • I know this has been your practice for years and you have the added benefit of having your own chooks/chickens. What did you think of the research on pollutant mitigation in plants using egg shells?
      Thanks for commenting Don.


  2. I mix the egg shells with coffee grounds and sprinkle them around my hostas to deter slugs and I use egg shells around rose bushes, too. I have microwaved them at times but have never crushed them to a fine powder before tossing them in my compost bin where the red wigglers live. I’ll make sure I’m more careful about this in the future.

    Liked by 1 person

    • I notice many people are making use of their eggshells Clare. And you have added coffee grounds to the mix – such a valuable garden resource too. I remember seeing a program on television where coffee grounds were used to grow mushrooms. Apparently coffee grounds encourage good soil microbes, always a good thing in my book. I love the way we can share our thoughts and practices through the blog-o-sphere.

      Liked by 1 person

  3. Very interesting topic Robyn. Slugs, caterpillars, and snails are not my favorite slithery creatures but death by eggshells sounds so horrific I feel sorry for the poor critters.

    Liked by 1 person

  4. I try to remove them manually since I’m reluctant to use chemical sprays. And you’re quite right about allowing the feelings, Steph. Every gardener knows there are challenges. That’s half the appeal I think.


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